1. Field of Invention
The present invention relates to a Universal Mobile Telecommunications System (UMTS) packet network; and more particularly to channel quality indicator (CQI) reporting schemes for Universal Terrestrial Radio Access Network (UTRAN) long term evolution (LTE) in the third generation partnership project (3GPP).
2. Description of Related Art
In the long term evolution (LTE) UTRAN, the architecture is modified so that there no longer will be a radio network controller (RNC). This UTRAN long term evolution is also using orthogonal frequency division multiple access (FDMA) in the downlink, as well as adaptive modulation and coding. The frequency band is divided into resource blocks (RB) in order to allow multiplexing of users in the frequency domain. The latter opens up the possibility for utilization of frequency domain link adaptation (FDLA), the frequency domain link packet scheduling (FDPS), etc. Moreover, the current working assumption for UTRAN long term evolution (LTE) is that the UE should send CQls in the uplink for different resource blocks (RBs) in order to facilitate the frequency domain link adaptation (FDLA) and the frequency domain link packet scheduling (FDPS) in the downlink. The exact definition of the CQIs and the reporting of those from the UE to the serving cell is currently under discussion in 3GPP. One of the design objectives in 3GPP is to agree on a good trade-off between minimizing the signalling overhead from sending the CQIs in the uplink versus the potential gain from using FDLA and FDPS in the downlink. In particular, there is a need for a method, system or technique for reducing the CQI signalling overhead for the special case where pending Hybrid Automatic Repeat-Request (HARQ) retransmissions are scheduled in the downlink.
In operation, the CQIs per RBs from the users are used by the base station (Node B) to determine (i) which users are going to be scheduled, (ii) which RBs to allocate to the scheduled users, and (iii) which modulation and coding scheme (MCS) to use for the scheduled users (i.e. for FDLA and FDPS). On the other hand, having “complete” CQI information frequently reported from all users and RBs might potentially cause excessive uplink signalling load. In view of this, there is a need for a way to reduce the CQI information significantly for users who are about to be scheduled HARQ retransmissions, since the base station has reduced degrees of freedom for transmitting such, as compared to new transmissions.